Marine organism mystery solved by new discovery

marine protists (microbial eukaryotes)
marine protists (microbial eukaryotes)

Though invisible to the human eye, ocean microbes support all marine life, from sardines to whales

The ocean’s tiniest organisms consume carbon dioxide and produce oxygen on a planetary scale, making them easily as important as forests for our planet. New research, published in the journal Current Biology, attempts to discover more about them.

Understanding the inner workings of oceanic microbes could reveal how they will fare in the warmer, more acidic ocean, of the future. There’s also a mystery to be solved. It’s long been known that ocean microbes have a day-night cycle are in tune with each other. However, with only one cell and no eyes, how do they know when it’s day or night?

The research team collects samples in the North Pacific.
The research team collects samples in the North Pacific.
Image: Dror Shitrit/Simons Collaboration on Ocean Processes and Ecology

Researchers collected samples of seawater from the same locations every four hours, for four days. The samples contained plant-like algae, which absorb light for energy, as well as other single-celled plankton that gain energy by consuming other tiny organisms.

By analysing RNA filtered out of these samples, the team found that single-celled organisms in the open ocean use an array of genetic tools to detect light, even in tiny amounts, and respond. The study identified four main groups of genetic photoreceptors, many of them new to science.

Protists of the Atlantic under the microscope
Protists of the Atlantic | Image: Smithsonian Ocean

The microbes need to know when the sun is up because they gain energy and grow in size in sunlight, and at night, when the ultraviolet light is less damaging to their DNA, they undergo cell division. This genetic activity also uses light to trigger changes in the metabolism, growth, cell division and movements.

“Daylight is important for ocean organisms, we know that, we take it for granted. But to see the rhythm of genetic activity during these four days, and the beautiful synchronicity, you realize just how powerful light is,” said senior author Virginia Armbrust, a UW professor of oceanography.

Photograph of diatoms collected in Russia and arranged on a microscope slide in 1952 by A.L. Brigger
Photograph of diatoms collected in Russia and arranged on a microscope slide in 1952 by A.L. Brigger | Image: California Academy of Sciences

The discovery of these new genetic “light switches” could also aid in the field of optogenetics, in which a cell’s function can be controlled with light exposure. Today’s optogenetic tools are engineered by humans, but versions from nature might be more sensitive or better detect light of particular wavelengths, the researchers said.

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